Measurement of leakage resistance in electrolytic cell systems



Dec. 2, 1947. v. F. HANSON ,0 3

MEASUREMENT OF LEAKAGE RESISTANCE IN ELECTROLYTIC CELL sYs'raus OriginalFiled April 16, 1942 'INVENTOR. VICTOR E HANSON ATTORNEY Patented Dec.2, 1947 UNITED STATES PATENT OFFICE- MEASUREMENT OF LEAKAGE RESISTANCEIN ELECTROLYTIC CELL SYSTEMS Victor F. Hanson, Pasco, Wash, .assignor toE. I. du Pont de Nemours & Company, Wilmington, Del., a corporation ofDelaware 1 Claim. (01. 175-183) This invention relates to the operationof systems of electrolytic cells operating on direct current and moreparticularly to the location of ground faults in such systems.

Thi application is a division of my copending application Serial No.439.224. filed April 16, 1942, issued as Patent No. 2,347,408.

In systems of electrolytic cells a group or bank of electrolytic cellsusually consists of a number of cells connected in series, the ends ofthe bank being connected to a suitable source of direct current, forexample, a rotary converter. Normally in such systems, the entire directcurrent circuit is insulated from ground. However, in practice it isimpossible to maintain perfect insulation and under the best ofoperating conditions there is always likely to be a certain small amountof leakage of electric current to ground from various parts of the cellcircuit. So long as such leakage is small, it is not particularlydisadvantageous. However, if a fault occurs anywhere in the system whichpermits a considerable amount.

. sirable to promptly locate a point at which any such serious leakageof current occurs so that the condition may be quickly cured. Thelocation of such current leakage is often very difficult to find by anyvisual inspection and heretofore there has been no adequate method oflocating such faults except by means of visual inspection or laborioustests which require undue periods of time to accomplish. The problem ofdetecting and locating such ground faults is almost wholly confined tthe cell bank, since other parts of the D. C. circuit are relativelyeasy to maintain in substantially perfectly insulated condition.

An object of the present invention is to provide a quick and easy methodfor locating ground faults in electrolytic cell systems. Another objectis to provide a means for promptly detecting the existence of suchground faults and to determine the extent of ground leakage at suchfaults. Another object is to provide an improved method and apparatu formeasuring the resistance between an electrolytic cell circuit andground, and thereby to readily detect the existence and degree of anyground leakage. other objects will be apparent from the followingdescription.

The above objects are attained in accordance with the present inventionby periodically measuring the resistance between the electrolytic cell,D. C. circuit and ground and measuring the voltage at a selected pointbetween the cell circuit and ground and, from the results of theseperi-' odic measurements, determining the degree and location of thecurrent leakage by a simple computation. Various known electricalinstruments may be utilized for the purpose of making said measurementsand the present invention is not restricted to any particular method orapparatus for making such measurements. However, the efi'icacy of theinvention will depend upon the accuracy with which such measurements aremade and hereinafter certain preferred methods for making thesemeasurements and apparatus are described.

The extent of ground leakage is measured by the total resistance of thecell circuit to ground and this may be measured at any desired point inthe cell circuit. In order to locate the position of the ground faultaccording to my invention, the voltage measurement must be made at a se-3 lected point in the cell circuit. Ordinarily I prefer to measure thevoltage at the midpoint of a cell bank consisting of a group of cellsconnected in series.

If a cell system comprising a bank of an even numbenof cells, forexample, 8 cells connected in series, is perfectly insulated from theground, the

resistance between the cell system and ground will be infinity and thevoltage between the cell circuit me ured at the midpoint in the cellbank and the gr und will be 0. If now leakage to ground occurs, forexample, in one of the cells between the\midpoint and the positive endof the bank, a voltmeter connected to ground at the midpoint will show areading of negative voltage. Thus, the negative reading on the voltmeterwill indicate that the fault has occurred on the positive side of thecell bank. If new the resistance between the cell bank and the ground ismeasured, it will be found to be less than infinity and if the aforesaidfault is the only fault in the system, this resistance will be theresista cc of the fault and thereby indicate the extent of groundleakage.

However, as stated above. normally there will be a number of smallleakages in the cell system. usually more or less distributed throughoutthe entire cell bank. Such small leakages are not of Still seriousconsequence and usually may be disregarded. However, these smallleakages will result in a resistance to ground of the cell bank which isof finite quantity and a voltage to ground at the midpoint of the bankwhich will be only when the leakages are equal .on both sides of themidpoint. If, however, in such a normal cell system a large cell leakageoccurs at any point in the bank, the total resistance of the cell bankwill correspondingly decrease and there will be a corresponding positiveor negative reading on a voltmeter connected to ground at the midpoint.Therefore by periodically measuring the resistance and voltage asaforesaid, I am able to promptly detect any such large leakage bycomparison of the readings obtained. Moreover. I have found that I canpromptly locate the position of the fault by application of thefollowing formula:

where N=number of cells from the point at which the voltage was measuredto the position of the fault.

Eo=voltage to ground of the cell bank before fault occurred, measured ata selected point. E voltage to ground of the cell bank after faultoccurred, measured at the same point as E0.

Ro=resistance of the cell bank before fault occurred.

R=resistance of the cell bank after fault occurred.

e=voltage drop per cell.

The above formula assumes that the voltage drop (e) from cell to cell inthe series-connected bank of cells is substantially the same throughoutthe bank. This is substantially true for the conventional bank of cellswherein the electrolyte, current density and other cell characteristicsare substantially the same throughout the cell bank. The relativelysmall differences in individual cell voltages which may occur throughoutthe cell bank cause only a negligible error in the use of the aboveformula.

The extent of ground leakage at the fault is indicated by the resistancereadings, and can be determined in terms of the resistance of the faultby application of the following formula:

resistance of the fault.

In an electrotlytic installation which comprises a number of separatecell banks having cells connected in series, it is often preferable toutilize a single voltmeter or single resistance measuring instrument forthe entire group and this may be done by providing the necessaryconnections from the various cell banks to a multiple switch at theinstruments, which are placed in a central or convenient location.

For the utilization of my invention it is not essential that the voltagebe measured at the midpoint of the cell bank, provided that the voltageis measured at the same point before and after the occurrence of theground leakage fault which is thereby indicated and located. The value Nwill be the number of cells from the point at which the voltagemeasurements are made. The resistance of the cell bank to ground may bemeasured at any desired point, not necessarily the same point before andafter the occurrence of the fault.

The appended drawing is a diagrammatic illustration of an electrolyticcell system showing the application to such systems of devices formeasuring the voltage and resistance as above described.

The figure illustrates a particular device for measuring both thevoltage to ground and the resistance of the cell bank to ground. Thisconsists of voltmeter 5 provided with a shunt circuit which containsshunt resistance 6 and shunting switch 1 which may be a single pole,single throw switch, or any other conventional switch of suitabledesign. Shunt resistance 6 is a resistance of known value. When switch Iis open, the voltage to ground may be read from voltmeter 5. When switch'l'is then closed, the voltage as shown on the voltmeter will be all.-ferent because of the shunt resistance. The resistances of the cell bankto ground before and after occurrence of the fault then may bedetermined by computation from the following formulas:

E4 where Ez=shunted voltmeter reading (switch I closed) before faultoccurred. E3=voltage of cell bank to ground (switch I open) after faultoccurred. E4=shunted voltmeter reading (switch 1 closed) after faultoccurred. The location of the fault then may be determined as describedabove from the formula:

wherein: Eo=E1; and E=Ea.

By mathematical derivation, it is apparent that the value of N may alsobe determined without separately computing the values of R0, and R, i.e., by using the following formula:

One'disadvantage of the method of measuring the cell bank resistance asillustrated by the figure is that occasionally the voltage reading maybe zero because of balanced leakage conditions in the cell bank. In suchcases, it is necessary to change the location of the instrument so as totake the voltage readings at some point other than the midpoint of thecell bank.

I claim:

The method for measuring the resistance to ground in a system of directcurrent electrolytic cells which comprises measuring the voltage toground with a voltage measuring means of given resistance at a selectedpoint in said system, measuring the voltage to ground at the same pointwith a voltage measuring means of the same resistance as the first-namedvoltage measuring means while shunting a given portion of said currentfrom said point to ground where- 2,432,013 5 6 b the resistance toground may be computed fl om the formula: REFERENCES CITED 1 I, (I'7l- EThe following references are of record in the Ff 5 file of this patent:when: UNITED STATES PATENTS R the r es i s tance to gti'ouiog fir; soloNumber Name Date R the lemstyance m J; U51 CllCLll 7 1215867 Romaim 4mFeb. 13 1917 E1 the f Uh u t m 1,800,474 Scherer Apr. 14, 1931 E2 th t ameabuled n 1e Enun 700 94 y 2.208329 Morelock July 15, 1940 VICTOR E.HANSON.

